Undue wear to vital parts can be caused by poor guncare, or environmental conditions, but it can also be due to a manufacturing defect such as poor heat treatment. I've seen a lot of poor heat treatment in the Cap & Ball replica revolvers and older pocket or house pistols.

Just today I was examing a 1922 FN/Browning I've owned for many years but seldom fired.
Externally all metal surfaces look to be in near new condition. Theres no blurring of any of the markings so its never been refinished. All parts easily inspected in a basic field striping show no wear at all.
Despite its apparent excellent condition when I used the safety lever in its slide latch function something odd occurred.
I latched the slide back and then watched as the latch ever so slowly disengaged itself. I tried this several times and it did it each time like clockwork.
The mating surfaces are visible and to the eye show no wear and look to be at the proper angle.
I then checked the function of the safety and found that while it took a noticable amount of force to engage, it took very little force to disengage. Not quite floppy but far to easy.
So as it stands I figure its a matter of whatever form of detent this safety uses.
I'm a bit leery of disassembling the lock completely, till I find a tutorial on this model.
Like as not it will require a replacement part that will be very hard to find in new condition.

Since repairing a Savage with spread frame rails that would fire when the safety was disengaged without any contact with the trigger I now no this can and almost certainly has happened.
If a firearm discharges without the trigger being pressed then its due to a defect in the firearm.
If the person holding it has negligently pointed it at a person then he would be at fault if they are injured, but the injury would not have occured had that firearm not been defective.
A firearm might be pointed in what would appear to be a safe direction, yet the bullet may still end up going in an unintended direction.
In the case of a SKS that slamfired and went full auto, the rifle was not pointed at anyone, yet the last several rounds of that unintended full auto burst destroyed a man's head.
Some AD's involving defective Glocks have injured persons not in the same room with the pistol. One SKS slamfire killed a man sleeping on another floor of the house.
A firearm never designed for full auto bursts can jump out of one's hands if it cut loose unexpectedly. The person holding it at the time would not be responsible for loosing control of the weapon due to such an unpredictable occurance. The fault would lay with the condition of the firearm or ammunition.